Support member types hierarchy

[slaFFik]

Would super-duper nice to have ability to classify users under sub-types.

Like:

- teachers:
--- maths
--- history
--- physics
- students:
--- whatever
--- else

W are using taxonomy for that, so DB supports that out of the box. Now would be nice to just extend the code to receive parent_member_type (id or slug) when setting member type.

[boonebgorges]

Data storage is the easy part :) What would this change mean for users?

• Would directory URLs be affected? example.com/members/type/teachers/maths/? or maybe example.com/members/type/teachers-maths?
• Presumably we'd need a "parent" dropdown when creating/editing a member type, pending #7181.
• In the member type metabox, we'd probably want the display to be hierarchical, as in your ticket description.
• Anything else?

[dcavins]

What would the behavior be? Would all members of the type "history" also be members of the type "teachers"? Could members still be of the parent type only, like "teachers," but have no subtype?

I'm thinking the default behavior of member types is more straightforward than in hierarchical groups, but at least with groups, people have a number of different ideas about the levels should interact. What are you thinking?

[DJPaul]

We need some more discussion about whether we want the feature. Given a lack of comments in the last 3 months, I suspect there is not being enough contributor interest to have this change made. If nothing happens in a few weeks, we'll close the ticket.

[slaFFik]

If this feature lands into core, I see it to have url example.com/members/type/teachers/maths/ as this is how parent/child terms work in WordPress.
Dropdown on user editing page and list of users in wp-admin area should be updated as well to include this hierarchy.
I assume children member types should behave the same as children categories - user can be assigned to a child only (although visible when filtered by parent), and can be assigned to a parent only.